<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>购物车</title>
    <style>
        #shoppingCart {
            box-sizing: border-box;
            margin: 100px auto;
            border-collapse: collapse;
            text-align: center;
            border: 1px solid rgb(250, 5, 46);
        }
        
        #shoppingCart thead {
            color: white;
            background-color: rgb(247, 17, 93);
        }
        
        #shoppingCart tfoot {
            text-align: right;
            color: white;
            background-color: rgb(247, 17, 93);
        }
        
        #shoppingCart tr td {
            width: 250px;
            padding: 10px;
        }
        
        #shoppingCart tr td input {
            width: 30px;
            height: 30px;
            text-align: center;
            font-size: 18px;
            outline: 0;
            border: 1px rgb(239, 239, 239) solid;
        }
        
        #shoppingCart tr td input[name='number'] {
            width: 100px;
        }
    </style>
</head>

<body>
    <table id="shoppingCart" border="1" width=1000 height=500>
        <thead>
            <tr style="height: 50px;">
                <th>商品</th>
                <th>单价</th>
                <th>数量</th>
                <th>小计</th>
            </tr>
        </thead>
        <tbody>
            <tr class="num">
                <td>相机</td>
                <td class="price">8</td>
                <td>
                    <input type="button" name="minus" value="-">
                    <input type="text" name="number" value="0">
                    <input type="button" name="add" value="+">
                </td>
                <td class="subtotal">0</td>
            </tr>
            <tr class="num">
                <td>相机</td>
                <td class="price">10</td>
                <td>
                    <input type="button" name="minus" value="-">
                    <input type="text" name="number" value="0">
                    <input type="button" name="add" value="+">
                </td>
                <td class="subtotal">0</td>
            </tr>
            <tr class="num">
                <td>相机</td>
                <td class="price">12.5</td>
                <td>
                    <input type="button" name="minus" value="-">
                    <input type="text" name="number" value="0">
                    <input type="button" name="add" value="+">
                </td>
                <td class="subtotal">0</td>
            </tr>
            <tr class="num">
                <td>相机</td>
                <td class="price">23</td>
                <td>
                    <input type="button" name="minus" value="-">
                    <input type="text" name="number" value="0">
                    <input type="button" name="add" value="+">
                </td>
                <td class="subtotal">0</td>
            </tr>
        </tbody>
        <tfoot>
            <tr style="background-color: white; height: 10px;"></tr>
            <tr style="height: 50px;">
                <td colspan="3">已选中商品:<span id="sum">0</span>个</td>
                <td>合计费用￥<span id="total">0</span></td>
            </tr>
        </tfoot>
    </table>
    <script>
        /**
         * num:商品数量
         * add:+
         * minus:-
         * number:数量
         * price:单价
         * sum:总数
         * total:总价
         * subtotal:小计
         **/
        let num = document.querySelectorAll(".num"),
            add = document.querySelectorAll("[name='add']"),
            minus = document.querySelectorAll("[name='minus']"),
            number = document.querySelectorAll("[name='number']"),
            price = document.querySelectorAll(".price"),
            sum = document.querySelector("#sum"),
            total = document.querySelector("#total"),
            subtotal = document.querySelectorAll(".subtotal");

        //数量改变
        for (let i = 0; i < num.length; i++) {
            add[i].index = i;
            minus[i].index = i;
            add[i].onclick = function() {
                //数量增加
                number[this.index].innerHTML = number[this.index].value++;
                let sign = this.index;
                operation(sign);
            }

            minus[i].onclick = function() {
                if (number[this.index].value > 0) {
                    //数量减少
                    number[this.index].innerHTML = number[this.index].value--;
                    let sign = this.index;
                    operation(sign);
                }
            }

            function operation(sign) {
                //小计改变
                subtotal[sign].innerHTML = price[sign].innerHTML * number[sign].value;
                sum.innerHTML = 0
                total.innerHTML = 0
                for (let j = 0; j < number.length; j++) {
                    //已选中商品数目改变
                    sum.innerHTML = number[j].value * 1 + sum.innerHTML * 1;
                    //商品总价改变
                    total.innerHTML = subtotal[j].innerHTML * 1 + total.innerHTML * 1;
                }
            }
        }
    </script>
</body>

</html>
